The present invention relates generally to an improved fluid-sampling system and method and, more particularly, to a method and apparatus for taking serum samples, such as samples of blood, spinal fluid, or the like, and placing them in chemical reagents for analysis.
The chemical analysis of a serum, for example, for the presence of sugar, albumin, or some other medically significant factor, is a vital part of medical diagnosis. Testing for various serum constituents is typically accomplished by combining a sample of the serum with one or more specific reactive chemicals or reagents and, after all chemical reactions are completed, by determining the light transmittance value of the completed test chemistry with a spectrophotometer or the like. The light transmittance value is used to calculate the optical density of the test chemistry and to derive the percentage concentration in the serum of the constituent of interest.
In performing a serum analysis, it is desirable to use the smallest possible quantity of serum for each particular test being undertaken. In many cases, only a very small amount of serum is available for the test; for example, spinal fluid specimens or blood specimens from pediatric or geriatric patients. In other cases, it is desirable to perform a number of different tests on a particular serum specimen; and it is necessary that there be enough of the serum available to conduct all of the tests. Also, the greater the quantity of serum used for a particular test, the greater the quantity of the reagents that must be used; and since many reagents are quite expensive, this can significantly increase the overall cost of the analysis.
At the present time, a large portion of the serum analyses being conducted are performed by automated systems. In performing such tests, it is essential that precise quantities of the serum and the appropriate reagents for the tests be mixed together in the correct proportions to ensure an accurate result when the test chemistry is analyzed. Most automatic systems currently on the market, however, are simply not able to achieve this necessary precision when only a very small quantity of a serum is used. Thus, notwithstanding the desirability of using the smallest possible quantity of a serum sample in each test, most automated systems currently in use are severely limited by the accuracy and precision of the measuring or metering means used in the system.
An automatic chemistry-analyzing system is disclosed, for example, in commonly assigned U.S. Pat. No. 3,901,656. In commonly assigned, co-pending U.S. patent application Ser. No. 304,384 filed on Sept. 22, 1981, and entitled ULTRA MICRO PRECISION FLUID METERING DEVICE, an automatic chemistry analyzer is disclosed that describes the use of a Bourdon pump to withdraw liquid from a first container as a sample having a definite size and to dispense the sample into a second container. More specifically, the Bourdon pump in the above-identified patent application is designed to provide samples in preselected increments of size. The size of the sample is determined by energizing one or more of a plurality of chambers of differing sizes by exerting pressure upon a surface of one or more of the chambers, and the sizes of the samples available are fixed by the sizes of the chambers built into the pump.
In many automated systems, a plurality of serum specimens are supported in individual containers on a turntable or other conveyor means; and a sample of the specimen to be tested is taken from the appropriate container by a sampler assembly when that container is in the proper transfer position relative to the sampler assembly. If it is desired to perform two tests on a particular serum, it is usually necessary to wait until the conveyor means has returned that particular serum specimen to the transfer position so that a second sample of the serum can be taken from the container.